CorpusHuman Anatomy
SkeletalMembrane

Periosteum

Periosteum

The vascular, richly innervated connective-tissue membrane covering the external surface of bones except at articular surfaces. Its inner layer contains osteoprogenitor cells responsible for appositional growth and fracture repair.

Long Bone — Structure Synovial Joint — Structure

Overview

The periosteum has two layers. The outer fibrous layer is dense irregular connective tissue carrying blood vessels, lymphatics and sensory nerves; it is continuous with tendons, ligaments and joint capsules. The inner cambium (osteogenic) layer contains osteoprogenitor cells and osteoblasts that lay down new circumferential lamellae — the mechanism of appositional growth in width and of external callus formation after fracture. The cambium layer is thick and active in children and becomes thin in adults.

Periosteum is anchored to the bone by perforating (Sharpey) fibres — bundles of collagen that penetrate the outer circumferential lamellae, especially where tendons and ligaments insert. It is absent over articular cartilage, at sesamoid surfaces and where tendons insert directly via fibrocartilaginous entheses. Unlike bone itself, periosteum is exquisitely pain-sensitive, which accounts for the pain of fractures, shin splints and bone tumours.

In children the periosteum is thick and loosely attached, so fractures often remain partially splinted (greenstick fractures) and heal rapidly with abundant callus.

Location

External surface of all bones except articular surfaces.

Parts & subdivisions

  1. Fibrous (outer) layer
    Dense irregular connective tissue with vessels and nerves; blends with tendons and ligaments.
  2. Cambium (osteogenic, inner) layer
    Osteoprogenitor cells and osteoblasts; prominent in growing bone.
  3. Perforating (Sharpey) fibres
    Collagen bundles anchoring periosteum, tendons and ligaments into the cortex.

Anatomy

Innervation

Rich sensory supply from nerves to adjacent muscles and joints.

Arterial supply

Periosteal arteries, which anastomose with nutrient (medullary) branches via perforating canals.

Function

  • Appositional growth of bone in width
  • Fracture repair (external callus)
  • Vascular supply to the outer third of the cortex
  • Attachment for tendons and ligaments
  • Sensory innervation (pain, pressure) of bone

Clinical significance

Periosteal reaction on imaging

Elevation of periosteum by pus, blood or tumour stimulates new bone: smooth/lamellated reaction in benign processes; "onion-skin" (Ewing sarcoma), "sunburst" spiculation and Codman triangle (osteosarcoma) in aggressive lesions.

Subperiosteal haematoma

In scurvy and non-accidental injury in infants, bleeding beneath the loosely attached periosteum later calcifies.

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.